Multiplex signaling system



Jan. 2, 1940.

P. MERTZ MULTIPLEX SIGNALING SYSTEM Filed Feb. 25, 1938 /NVENTQR P.MERTZ' 3-Shee1;s-Sheet 1 FIG 2 YATTORNEY Jan. 2, 1940. P, MERTZMULTIPLEX SIGNALING SYSTEM Filed Feb. 25,- 1938 v3 Sheets-Sheet 2 4a x91 l 48 f 2:2 7

' nfl i .39d J osc "5 /NVENTOR By P. MERTZ AT TORNEV Jan. 2, 1940.

P. MER-rz 2,185,693

MULTIPLEX SIGNALING SYSTEM Filed Feb. 25, 1938 3 Sheets-Sheet 5 FIGS AMP

P. MERTZ A T TORNE Y Patented Jan. 2, 1940 UNITED STATES PATENT GFFHCEMULTIPLEX SIGNALING SYSTEM Application February 25, 1938. Serial No.192,471

5 Claims.

This invention relates to multiplex transmission of messages andparticularly of message',

waves comprising bands of frequencies, for example speech or musicwaves, television or simi- 5 lar Waves, the multiplexing being on a timedivision basis.

An object of the invention is tosecure improved multiplex transmissionof the type indicated, by means of simplified and improved apparatus.

In the transmission of speech and music or other complex waves it isnecessary to reproduce at a receiving point a Wave which is changingfrom instant to instant in frequency, amplitude and phase in the samemanner as the wave at the transmitting point. Moreover, it is necessaryto avoid as far as possible the production of Waves other than thespeech or music waves, such as all forms of noise and distortion,including cross-talk. In a time division multiplex system the speed atwhich the sampling of the different message Waves is to occur has to Abehigh in comparison with the highest essential message Wave frequency,which in the case of speech or music, for example, is several thousandcycles per second. The sampling at the transmitter and the separationand reconstruction at the receiver must be carried out in closesynchronism and especially Without an appreciable cumulative timedifference in order to avoid cross-talk or the actual crossing ofchannels. These requirements impose severe restrictions upon theapparatus to be used in a time division multiplex system.

En accordance with this invention distributors of the electronic typeand of special construction are provided at the sender and receiver,which cooperate tc effect the analysis and reconstruction or' the Wavebands constituting the messages. These distributors incorporate suitablemultiple terminals for the incoming and outgoing circuits and controlmeans for varying the electron stream in accordance with message wavesin such a way as to sample the respective message n ri Waves at thetransmitter and separately recon- The various features and objects ofthe invention will appear`more fully in the following detaileddescription of an illustrative embodiment of the invention as shown inthe accompanying drawings.

In the drawings, Fig 1. is a simplified schematic circuit sketch of. atwo-way terminal station for a system according to the invention;

Fig. 2 is a schematic circuit diagram of the transmitter; l

Fig. 3 is a' view of. the electrode structure looking toward the rightin Fig. 2 from the plane 3 8;

Fig. 4 is a schematic circuit diagram of the receiver;

Fig. 5 is a schematic circuit diagram of the electrode structure of thereceiver and of the synchronizing channel receiver; and

Fig. 6 is a partial view of an alternative type of receiver tubestructure.

Referring to Fig. 1, a plurality of telephone lines. are indicated atIt, I9 and 20 as coming into the station shown in this figure, theselines being indicated by single line circuits for simplicity. Theselines are associated with transmitting electron distributor l0 andreceiving elec- `tron distributor 50 which are respectively associatedwith transmitting radio terminal 2t and receiving radio terminal 58.While radio transmission is indicated in this figure, it will be obviousthat the transmission could take place equally Well over line conductorsof any suitable type.

The incoming telephone lines are associated with the transmitting tubei@ by circuits i3, M and i5 connected to the respective telephone linesby means such as the usual hybrid coil and line balancing network shownat il, il. Low-pass filters, such as it, are included in theseconnections to suppress currents of frequencies higher vthan the highestspeech frequency which is to.

be transmitted. The individual lines i3, id and i5 lead to individualgrids l, 8 and ii in the distributor tube i0. (The structure ofdistributor tubes it and 50 will be more fully disclosed in connectionwith the subsequent figures.) A common anode I2 cooperates with theindividual grids. `A suitable rotating field is produced under controlof oscillator 5 in a manner to be described for rotating the cathodebeam indicated at II over the grids in succession such that the outputcurrent from the distributor tube l0 is composed of small fragmentstaken successively from the speech currents present in lines I3, I4 andI5. The scanning frequency is high compared to the highest speechfrequency to be 55 transmitted so that the output current; is seen tocomprise high frequencies. These output currents are transmitted throughany suitable connecting circuits, such as a coupling circuit 22 andamplifier 23, to the radio transmitter 24.

The receiving distributor 5|) differs mainly from the transmittingdistributor I0 in having a single l grid 55 and individual anodes 52, 53and 54. The received waves from the distant multiplex transmitter areamplified at 51 and impressed through any suitable coupling circuit 56across the grid and cathode 55 and 59 of distributor tube 50. 'I'heoscillator 5' causes the beam shown at 5| to rotate and intercept theplates 52, 53 and 54 in synchronism with the scanning motion of the beamat the distant transmitter. The grid 55 meanwhile varies the intensityof the beam 5| in accordance with the instantaneous amplitude of thereceived waves. There is thus produced in the output current, from eachindividual anode such as 52, a current impulse corresponding in allrespects to the fragment of the speech eX- isting atthe same instant inthe corresponding transmitting line at the distant station. Thesereproduced fragments of speech are transmitted through low-passfilters,A such as 60', and ampliers such as 60', into the respectivelines 6|, 62 and 63, leading to the hybrid coils in the respectivetelephone lines |8, |9 and 20. Where the phase shift between terminalsis sufficiently small, or can be suitably compensated a singleoscillator may serve in place of the two shown at 5 and 5.

While only three telephone lines are indicated in Fig. 1 associated withthe transmitting and receiving distributors, it is contemplated that amuch larger number of lines might in practice be' arranged for multiplextransmission in the same manner, the actual number depending upon thedesign limitations of the tubes or other requirements.

Referring now to Fig. 2, the transmitting distributor tube I0 is shownin somewhat greater detail. The tube is shown provided with a' suitablecathode 36 in the form of a filament heated from battery 42. In axialalignment with the filament is the accelerator tube 31 positively biasedfrom battery 43. Any other suitable form of electron gun may be usedincluding so-called' electron lenses of known type. 'I'he beam emergingfrom the accelerator tube 31 or other gun structure passes between pairsof plates 38 'and 39 situated at right angles to each other and thencepasses down the tube to the opposite end where the various grids and theanode are located. One pair of deector plates 38 is connected acrossresistance 4D while the opposite pair 39 is connected across condenser4| in ac- .cordance with the usual practice, the resistance and capacitybeing bridged across the terminals of the oscillator 5. A rotating iieldis thus produced. 'I'he individual grids 1, 8, and 9 are connected byleads 28, 29 and 30, through individual secondary windings of repeatingcoils, one of which is shown at 26 to a common, grid 35 extending allthe way across the tube, this latter grid being preferably grounded.Grid 35 is a retarding grid and is preceded by an accelerating grid 34having a positive potential applied from battery 44. I'he retarding grid35 produces a region of relatively low velocity in which the controlgrids are placed so that they are enabled to exert a more completecontrol over the anode current. Anode I2 is shown provided with suitableanode battery 45 which is connected in series with coupling impedance45. Outgoing amplifier 23 is connected across this coupling impedance.'I'he f control grids are each preferably shielded by being completelyenclosed in individual screens 3|, 32, 33, which are preferably atground potential. These screens provide electrical isolation of theindividual control grids to guard against crosstalk eiects that mightotherwise resultfrom the close positioning of the control grids. Tube I0in this figure is indicated@diagrammatically as embodying more thanthree control grids. While elements 3|, 32, 33 and 35 are shown as atground potential, it is within the invention to bias any of theseelements as required. P

A typical arrangement for the control grids of the tube ||l is shown inFig. 3. The grids are arranged in a circle with a suitable space betweeneach two successive grids. Common anode I2 is shown back of the grids.Two special grids 48 and 49 are shown in this figure connected to polesof respectively opposite polarity of batteries 4B' and 49'. These twogrids serve for synchronizing purposes in a manner presently to bedescribed. The orbit of the electron beam past the grids is indicated bya broken line.

Referring to Fig. 4, the receiving electron distributor 50 is shown indetail. This tube comprises a suitable electron source in the form offilament 66 heated from battery 68. Accelerator tube 61 is given apositive potential from battery 69. As in the case of tube I0 any othersuitable electron gun structure may be used. Oscillator 5' is connectedacross resistance 10 and capacity 1| and the pairs of plates 12 and 13produce a rotating eld for the beam 5|. Located between the cathode 66and accelerator tube 61 is control grid 55 shownv connected to the'output of receiving amplier 51 following equalizer 15. The individualanodes 52, 53, etc. are connected to one terminal each of the respectivereceiving circuits, the opposite terminals of which are connected incommon to a guard'plate 14 and to the positive pole of anode battery 69.Guard plate 14 prevents'electrons not caught by anodes 52, 53, etc. fromaccumulating into a space charge.

'I'he appearance of the anode structure looking to the right of the line5-5 of Fig. 4 is shown in Fig. 5. It is seen that the individual anodesV52, 53, etc. are each narrower than the corresponding grids of thetransmitting tube and are spaced apart so that the anguular distancebetween their centers is the same as that between the' grids of thetransmitting tube. Slight deviations in phase between the transmitterand receiver are thus allowed for. shown at and the position of the beamis indicated at the instant corresponding to exact synchronism with thetransmitting tube of Fig. 3.

The circuit of the oscillator 5 is shown in detail in Fig. 5 ascomprising two triodes 8| and 82 having their plates connected throughrespective resistances 86 and 81 across the terminals of tuningcondenser 95. The tuning inductance is shown as comprising the twohalves 90 andv 9| mounted on magnetic core 93. The cathodes areconnected together and to the heating battery 92 in series With theresistances 88 and 89. The plates are connected to plate battery throughprimaries of output transformer 83, the secondary of which leads througha narrow bandpass lter 84 'to the phase Splitting circuit 10, 1|. Filter84 suppresses harmonics so that a single frequency wave is supplied tothe field plates. Phase splitting circuit 10, 1| acts similarly to theelements 40, 4| of previous gures but is arranged A specialsynchronizing anode is' to pass direct current so as to enable thenormal potential of the deflection plates to be fixed. as noted below.

For synchronizing purposes the oscillator 5' is provided with a winding94 on the magnetic core 93 of the tuning inductance to permit smallchanges in the frequency of the generated oscillations under control ofcurrent in the winding 94 which changes thedegree of saturation of core93 and, therefore, the value of the inductance 9D, 9|. f

For this purpose a circuit is connected across special synchronizingsegment 88 and anode battery 69 comprising conductors 99 and |80.leading to direct current amplifier 91 `(if used) and low-pass lter 96and thence to the winding 98.

The operation of the synchronizingy channel will be apparent fromconsidering Figs. 3 and 5 together, Fig. 3 being assumed for thispurpose to be the transmitting distributor at a distant station withwhich the distributor of Fig. 5 at the home station is to be kept insynchronism. The oscillators 5 and 5' are assumed to generate waves oinominally the same frequency and the beams and 5| are assumed to be atthe' instant under consideration in exact phase with each other as shownin the drawings. beam li of the transmitting distributor passesclockwise across the grids 58 and i9 a sudden reversal of line currenttakes place since grid 88 has a high negative potential and grid 89 ahigh positive potential. This sudden reversal of line currentcorresponds to the instant when the beam passes off from grid 48 ontogrid 19.`

It may be of interest to note that this reversal is sent without thenecessity of transmitting a direct current component. If the beam 5l ofthe receiving distributor reaches the middle of segment 8U at theinstant when the reversal of line current is received, it is obviousthat the beam has traversed the first half of the segment 88 when itscontrolling grid 55 has a high negative value and will traverse thesecond half of segment 38 when control grid 55 has a high positivevalue. Under these conditions a dennite average value of direct currentis supplied to the winding 98 from battery 69', as determined by thesynchronizing pulse.

Ii, however, the receiving beam 5| is slow the current in circuit 99,|88 is greater than average since beam 5| traverses the greater portionof segment 89 during the time when grid 55 is highly positive under theinfluence of grid #i9 at the distant transmitter. Conversely, if thebeam 5i is fast the current transmitted into circuit 99, lill! will belower than average. These values of current are properly related to thevariations in the tuning inductance of the oscillator 5 to causecompensating variations in its frequency such as to advance the beam 5|or to retard it by the proper amount to restore exact synchronism. Theadvancing or retarding action may take place over a number ofdistributor cycles.

I have shown in Fig. 6 another type of ampliner for the synchronizingimpulses. In this ngure a portion of a tube is shown which except forits anode end structure may be entirely similar to the tube 50 of Fig.4. The tube 58', however, incorporates back of the guard plate 14 anelectron multiplier type of amplifier comprising secondary emitterplates |80 to |83 and anode |84. The guard plate 'Hi is shown providedWith an aperture at the proper point for permitting the beam 5| tostrike the rst emit- AS theter platev |80 which corresponds in angularposition to the anode 8|) of Fig. 5. By means of the successivelyhigher'potentials` applied to the successive plates |80 to |83 frombattery |88 over conductors |85 to |88, respectively, second-" thenormal potential of the deflector plates would ordinarily be used in thecircuits shown in each of Figs. 1, 2, 3, and 4 in place of theungrounded connections that have been shown for simplicity. Suchconnections may follow `those shown in more detail in Fig. 5 where thegrounded biasV battery lill is connected to the mid-point. of thesecondary winding of the oscillator output coil, and the phase splittingcircuit is arranged in bridge configuration to provide direct currentpaths to ground from all deflector plates.

While a preferred embodiment of the invention has been illustrated anddescribed, it is to be understood that the invention is not limited tothe specific details but that the'invention includes modications thatmay be made within the scope of the appended claims.

What is claimed is: l

1. In multiplex telephony, in combination, a cathode ray tube havingmeans to produce a cathode beam, a plate against which said beam isdirected, and a plurality of grids lying in a. plane normal to the axisof the tube and positioned to be scanned by the beam in its movements, aplurality of screens individually enclosing said grids and electricallyconnected together within said tube and to ground, means to move thebeam to scan said grids in cyclic order at a cyclic frequency high incomparison with the highest essential speech frequency, a plurality oftelephone transmitting circuits ccupled individually to the grids forplacing speech potentials upon the respective grids, and an outgoingcircuit from said plate.

2. In multiplex signaling, in combination, two cathode beam tubes,having beam deflecting field members, at respective stations,oscillators at said stations for producing rotary fields for said beamdeiiecting members, a pair of grids in the tube at the transmittingstation in a plane normal to the tube axis, in position /to be scannedby the beam, means placing a difference of potential between said grids,an anode common to said grids and an output circuit connected to saidanode whereby the beam in scanning said grids produces an abrupt changeof output current in passing from one grid to the next, means totransmit energy resulting from said abrupt change of output current tothe receiving station, a grid in the tube at the receiving station,means controlling its potential by the received energy, an anode ofsmall angular width in said tube at the receiving station, and meanscontrolled by the current to said anode for producing small correctivechanges in the frequency of the oscillator at the receiving station.

3. A multiplex system having transmitting and receiving stations withprovision for the'transmission of energy between them, comprising at thetransmitting station a yplurality of lines, an evacuated tube jhaving ananode and a plurality of individual grids or control members, said linesterminating individually on said respective grids, said tube havingmeans for producing a cathode beam movable to scan said grids, and, atsaid receiving station, comprising a cathode beam tube including aplurality of anodes to which receiving lines are connected similar innumber to the transmitting lines, means to control the beam intensity inaccordance with energy received from the transmitting station, means,including an oscillator at said receiving station, for synchronouslymoving said beams over their respective grids and anodes and furthercomprising a pair of special grids side by side in' the tube at saidtransmitting station with means to impress a steady diiierence ofpotential between the grids of said pair, a special anode in said tubeat the receiving station corresponding in angular position to saidspecial grids, whereby the average current to said special anode is a,function of the departure from phase coincidence of the said beams and acircuit for utilizing variations in the current to said special anode tocontrol the period of said oscillator to counteract departures fromphase coincidence between said beams.

4. In multiplex signaling, in combination, two cathode beam tubes atrespective transmitting and receiving stations, means at said stationsfor producing similar movement of the cathode beams in the respectivetubes including at the receiving station an oscillator, a pair of gridsin the tube at the transmitting station positioned to be scanned inclose succession by the beam in the tube at that station, means placinga difteraisance ence of potential between said grids, an anode and anodecircuit common tosaid grids whereby a change in anode current isproduced by the scanning of said grids, means to -transmit energycorresponding to saidchange in anode current to the receiving station, agrid in the tube at the receiving station and a circuit for controllingits potential in accordance with the energy so transmitted, a segmentalanode in the tube at the receiving station, said last-mentioned gridcontrolling the current to said anode, and circuit means operativelyrelating said anode and said oscillator for controlling the period ofsaid oscillator in' direction and magnitude to maintain said beams insynchronism and phase with each other.

5. In the transmission of intelligence employing beam tubes ascommutators, the method of keeping the beam in a receiving' tube inexact step with the beam in ai transmitting tube comprising locallycontrolling the movement of the beam in the receiving tube, causing thetransmitting tube to produce an abrupt change in its output energy at aspecified point in the movement ofits beam, transmitting energy inaccordance with said abrupt change to the receiving tube, controllingthe beam intensity of the receiving tube to produce normal, greater thannormal or less than normal output current depending upon existence ofexact agreement in movement of the two beams, departure from exactagreement in one direction or departure from exact agreement in theother direction,

as the case may be, and varying the rate of movement of the beam in thereceiving tube in accordance with departures from the normal strength ofsaid output current, in such. direction as to bring said beams intostep.

PIERRE MER'IZ.

